Heretofore, in an optical information recording medium such as a CD (Compact Disc) or DVD (Digital Versatile Disc), an organic coloring material has been mainly used as the material of a recordable optical information recording medium. The reason is that it is relatively easy to maintain compatibility with a ROM (Read Only Memory) demanded to have relatively high reflectance from the viewpoint of standard in a wavelength region of a laser beam used for recording/reproduction in the case of using the organic coloring material. Further, since a recordable optical information recording medium is obtained only by a simple process of spin-coating an organic coloring material and, after that, forming a reflection layer by sputtering, it is advantageous also from the viewpoint of manufacture cost of facility investment or the like.
However, when the wavelength of a laser beam used for recording and reproduction becomes shorter and a laser beam (having a wavelength of about 400 nm) of a wavelength range of blue-violet comes to be used, the circumstances are changing. Specifically, it is not easy to synthesize an organic coloring material which can be adapted to the laser beam having the wavelength from the viewpoints of recording sensitivity and signal characteristics. The existing simple layer configuration of the optical information recording medium is also not easily adapted to the laser beam. Further, it has become apparent that unmaintained uniformity between lands and grooves due to manufacture of the recordable optical information recording medium by spin coating is disadvantageous also from the viewpoint of a push-pull signal, crosstalk, and the like in high-density recording.
To address the demands, an inorganic recording material is often used in place of the organic coloring material. A recordable optical information recording medium using an inorganic recording material has been being studies but has not been practically used for reasons that compatibility with a ROM having high reflectance is low and an expensive sputter apparatus capable of forming a multilayer film from a material is necessary. However, generally, dependency of an inorganic recording material on the wavelength of a laser beam used is not higher than that of an organic coloring material. In addition, formation of multiple information recording layers (by forming a plurality of information recording layers, the recording capacity of an optical disk is increased by twice or more without enlarging the size) which is often performed in recent years is easily performed more than the case of using the organic coloring material. Consequently, use of the inorganic recording material is becoming the mainstream as the next-generation optical recording material in place of the organic coloring material and is also practically used.
Inorganic recording materials of various types are proposed. For example, a recordable optical information recording medium using a recording layer of a form formed by making two or more thin films made of different metals or half metals in contact with each other is proposed (refer to patent document 1). In the recordable optical information recording medium, a multilayer film is partly alloyed with heat generated by irradiation of a laser beam to form a single film, thereby forming a recording mark. As applications of the method, various forms with different materials are also proposed (refer to, for example, patent document 2). A recordable optical information recording medium using an oxide-based compound for a recording layer is also proposed (refer to, for example, patent documents 3 and 4).
However, it is far from the situation that those media sufficiently satisfy conditions necessary for a recordable optical information recording medium. Specifically, a recordable optical information recording medium is desired to have a characteristic that recorded information is stably stored in an initial state for long time (archival characteristic), a characteristic that a signal is not damaged by a laser beam for reproduction at the time of signal reproduction (reproduction stability), a characteristic that quality is not changed by normal long-term storage and the write characteristic is held (shelf characteristic), and the like. However, it is far from the state that each of the conventional recordable optical information recording media has all of the characteristics. In addition, from the viewpoints of manufacture cost of a recordable optical information recording medium and assurance of a margin in the manufacture process, it is also demanded that the number of layers constructing the recordable optical information recording medium is as small as possible, and the process is simple. Or more specifically, from the viewpoints of the recording/reproduction characteristics, sufficient sensitivity and reaction speed is also demanded so that a recording/reproduction signal which is excellent in a wide range of linear speeds is assured.
There is proposed a recordable optical information recording medium using an inorganic recording material, including a recording layer having a composition expressed by SbaInbSncZndSieOfSh where a>0, b>0, c>0, d>0, e>0, f>0, h>0, and a+b+c+d+e+f+h=100 (refer to patent document 5). There is also proposed a recordable optical information recording medium using a recording layer having a composition expressed by SbaXbSncZndSieOfSh where X is an element selected from In, Ge, Al, Zn, Mn, Cd, Ga, Ti, Si, Te, Nb, Fe, Co, W, Mo, S, Ni, O, Se, Tl, As, P, Au, Pd, Pt, Hf, and V where a>0, b>0, c>0, d>0, e>0, f>0, h>0, and a+b+c+d+e+f+h=100 (refer to patent document 6).
Further, there is proposed a recordable optical information recording medium having a plurality of information recording layers, using a recording layer containing at least one metal M selected from the group consisting of Ni, Cu, Si, Ti, Ge, Zr, Nb, Mo, In, Sn, W, Pb, Bi, Zn, and La and an element X which is bonded to the metal M by being irradiated with a laser beam for recording, thereby generating crystal of the metal M and the compound (refer to patent documents 7 and 8).